Increasing the Resilience of the Tree Canopy Following an Ice Storm

After a major ice storm in 1998, the City of Brampton embarked on an ambitious program of tree planting to help recuperate losses to the tree canopy while simultaneously increasing resilience to such events in the future. The 1998 Ice Storm caused significant damage across Southern Ontario and Quebec. It was officially recorded as the first storm in Canada to cause over a billion dollars in losses and was responsible for 35 deaths, 935 injured persons, and the temporary displacement of roughly 600,000 across the affected area. This storm also caused widespread devastation to the local tree canopy as the ice accumulating on the branches of trees eventually caused branches to break off or the tree to topple entirely. Rehabilitating the tree canopy has been on ongoing process that has suffered some setbacks, such as another major ice storm in 2013 that again caused extensive damage to the canopy, revealing problems with the tree selection process but also providing the opportunity to learn and refine the approach.

Understanding and Assessing Impacts

An ice storm is formed under a particular set of atmospheric conditions in which a layer of warm is sandwiched between two layers of cold air. Snow forms in the upper cold layer and passes through the warm air on its way towards the ground, melting into rain as it does so. This rain then passes through the lower layer of cold air but instead of freezing, it becomes supercooled. That is to say, the temperature of a drop of water will be below the freezing point (0°C) but will not have sufficient time to turn to ice. When this supercooled rain lands on a surface, it almost immediately freezes, coating the surface it landed on in a film of ice. These kinds of events are common in Canada. The reforestation program in Brampton was initiated in the wake of a major ice storm in 1998 and the city was again struck by another major ice storm only 15 years later in 2013. It is also likely that freezing rain and ice storms are going to be more common in the Winter months in Southern Ontario and Quebec, with some reports indicating the potential for a 40% increase in such incidents.

Identifying Actions

The damage sustained to Brampton’s tree canopy went beyond just the physical damage, it also a form of harm to the culture and identity of the city. Brampton had long considered the local vegetation a point of pride, so much so that one of the nicknames of the city is ‘the Flower City’ based on its long history of floriculture going back to the late 19th century. As a result of this, there was a focus on not just replanting the trees, but also a distinct focus on replanting the right type of trees. Prior to the 2013 storm, a lot of the trees planted in Brampton were selected primarily for their aesthetic purposes. Many of these trees were not well adapted to the weather and suffered very high mortality rates during the storm. Following the event, biologists and arborists were consulted in order to determine which trees were better suited for the local weather conditions; additionally, the was a greater focus on tree diversity as well. After a financial analysis, the city came to the conclusion that they would need to plant roughly 50,000 trees for about $1000 apiece following the 2013 Ice Storm. A $50 million price tag is no small matter for a city the size of Brampton, so they opted for a 10-year replanting strategy.

Implementation

Brampton’s tree planting strategy has not yet finished its 10-year planned length. One of the mechanisms by which the city promotes tree planting is through development bylaws that state for every new family home built by a developer, one tree must be planted. This bylaw exists in conjunction with, and as a supplement to, the city’s own tree planting efforts. One of the realized co-benefits from having a more diverse tree canopy is increases in the amount of shading available during extreme heat events. Officials contacted for this case study reiterated the importance of choosing a resilient tree canopy.

Next Steps

The City’s canopy restoration program is slated to end in 2025, but the principles of planting native species and ice storm resistant types of trees will remain part of the City’s overall approach.